Wavelength division multiplexing systems typically have multiple, separately modulated laser systems at a transmitter location. These laser systems are designed or actively tuned to operate at different wavelengths. When these laser emissions are combined in an optical fiber, the resulting wavelength division multiplexed optical signal has a corresponding number of separated channels. Along the transmission length, the channels may be collectively amplified by amplifier systems or gain fibers. At the receiving end, the channels are separated from each other to thereby enable detection by separate detectors.
The advantage of wavelength division multiplexing systems is that the transmission capacity of a single fiber can be increased. Modem wavelength division multiplexing systems have hundreds of spectrally separated channels per fiber. This yields increases in the data rate capacities of each fiber. Furthermore, the cost per bit of data in a wavelength division multiplexing system is typically less than in a comparative non-multiplexed system. This is because optical amplification systems required along the link are shared by all of the separate wavelength channels transmitted in the fiber. With non-multiplex systems, each channel/fiber would require its own amplification system.
However, there are difficulties associated with implementing a wavelength division multiplexing system. First, the transmitters and receivers are substantially more complex since, in addition to the laser emitters and receivers, optical components are required to combine the channels into, and separate the channels from, the wavelength division multiplexing optical signal. Furthermore, there is a danger of channel drift where the channels loose their spectral separation and overlap each other. This interferes with channel separation and demodulation at the receiving end.
Optical networks that have many wavelengths require wavelength control. Typically, wavelength control is performed at each laser source. At the laser source, a wavelength is sensed and then adjusted accordingly. In order to support this process, the system must provide either a plurality of wavelength sensing components or a switching network to present laser outputs sequentially to a single wavelength sensing component. Current wavelength sensing components sense only one wavelength at a time. The response of a first wavelength typically obscures the response of a second wavelength, which makes identifying the wavelength requiring adjustment and the direction of adjustment difficult. Thus there is a need for the ability to sense multiple wavelengths simultaneously in a single sensing device.